1. Field of the Invention
This invention relates to current limiting circuit breakers and, more particularly, to circuit breakers having a one turn in-line magnetic blowout coil to improve the performance of contact erosion, current limiting, and interruption ability.
2. Description of the Prior Art
Current limiting circuit breakers have been used successfully in recent years to limit these fault currents. They can reduce to tolerable levels both the peak fault currents (I.sub.p) and thermal energy (I.sup.2 t) that reach downstream equipment. Mechanical and magnetic forces that can destroy equipment are proportional to the square of the peak currents (I.sub.p).sup.2, and thermal damage is proportional to the energy let-through (I.sup.2 t). Current limiting devices not only perform the function of a circuit breaker and current limiting fuse, but are also resettable and reusable. These devices can also be effectively applied to motor control as well as power distribution systems.
Notwithstanding the foregoing, two major factors control how well current limiting occurs; namely, how quickly the contacts separate after initiation of a fault current, and how quickly the impedance of the air arc develops, more particularly, as the contacts separate and arc is drawn between them. The next stage in the current limiting process is to develop a high arc voltage. This is accomplished by stretching and blowing an arc off of the contacts into a set of deion plates by self-induced electromagnetic forces. When the arc hits the plates it is lengthened, split up, and cooled rapidly, which generates a high resistance arc. The arc is a circuit element and a nonlinear resistor with the arc voltage in phase with the arc current. The success of this approach requires a very high contact opening speed. The faster the contacts separate after initiation of the fault current, the shorter the dwell time of the arc acting on the contacts. Thus, the volume of melting and volatilization of the contact material is minimized.